JP2824091B2 - Powder coating resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of the Invention The present invention relates to a saponified ethylene acetate-vinyl copolymer (EVOH) having excellent gas barrier properties and solvent resistance that can be coated on metals, ceramics, glass and the like. A resin for powder coating comprising:

B. Prior Art Conventionally, powders such as polyethylene, polyamide and epoxy resin have been used as powder coating resins mainly for protecting metals from rust and solvents.

However, these resins have poor adhesion to metals and the like, and have insufficient gas barrier properties (especially oxygen and carbon dioxide gas) and solvent resistance, so that the coatings have to be thickened more than necessary, which is economical. There was a drawback that the properties were poor. Further EV
A method of coating an OH powder on a substrate by a method such as fluid immersion, spraying, or electrostatic coating is also known from Japanese Patent Publication No. 58-25702, but a melt index as disclosed in the examples of the publication is disclosed. If the resin has a low TS, the fluidity of the coating film at the time of melting is poor, making it difficult to smooth the coating film surface, and the uniformity of the coating film thickness is not sufficient.

C. Problems to be Solved by the Invention The present invention is to improve the adhesion to the substrate, to smooth the coating film surface, and to make the coating film thickness uniform, and to impart gas barrier properties and solvent resistance. Is what you do.

D. Means for Solving the Problems In order to solve the above problems, the present inventors have conducted various studies and found that the ethylene content is 20 to 60 mol%, the saponification degree of the vinyl acetate component is 99 mol% or more, and the MI (Load 2160g, temperature 1
EVOH (measured at 90 ° C.) of 5 to 60 g / 10 minutes was found to be excellent as a resin for powder coating.

EVOH used in the present invention has an ethylene content of 20 to 60 mol%.
Is important, and is preferably 25 to 50 mol%.
It is important that the degree of saponification of the vinyl acetate component is 90 mol% or more, and preferably 99 mol% or more. If the ethylene content of EVOH is less than 20 mol%, the properties of the saponified copolymer are close to those of PVA, and the water resistance and the gas barrier properties at high humidity are reduced. Since the number of hydroxyl groups in the saponified product is reduced, solvent resistance, adhesion to a substrate, and gas barrier properties at low humidity are reduced. If the degree of saponification is less than 90 mol%, the gas barrier properties and the solvent resistance are reduced.

Further, it is important that the MI of EVOH used in the present invention is 5 to 60 g / 10 minutes, and if the MI of EVOH is less than 5 g / 10 minutes, the melt fluidity is poor, and the smoothness of the coating film surface is poor. When the amount exceeds 60 g / 10 minutes, the melt fluidity is improved, but the melt tension is insufficient, and the melt flows easily from the substrate. This is clear from the examples and comparative examples described later.

In addition, EVOH powder has a particle size of 20 to 100 mesh (that is, 2
It preferably contains 80% by weight or more of those which pass through the 0-mesh section and do not pass through the 100-mesh section, and more preferably 80% by weight or more of 30 to 100 meshes. When a large amount of powder having a large particle diameter that does not pass through the 20 mesh node is used in large quantities, for example, a thermal spraying method tends to cause clogging of the nozzle portion, or the coating film surface tends to be uneven, making it difficult to obtain a smooth surface. On the other hand, when a large amount of particles having a small particle size that passes through the 100-mesh section are used, they are easily burned by the flame at the time of thermal spraying, and the cost required for pulverization becomes high.

The EVOH used in the present invention may be modified with a small amount, for example, 5 mol% or less of a copolymerizable monomer. Examples of the modifying monomer include propylene, 1-butene, 1-hexene, and 4-methyl-1. -Pentene, acrylic acid ester, methacrylic acid ester, maleic acid, fumaric acid, itaconic acid, higher fatty acid vinyl ester, alkyl vinyl ether, N-vinylpyrrolidone, N-n-butoxymethylacrylamide, vinyltrimethoxysilane, vinylmethyldimethoxysilane, Examples thereof include vinyldimethylmethoxysilane, N- (2-dimethylaminoethyl) methacrylamides or quaternary compounds thereof, and N-vinylimidazole or quaternary compounds thereof.

Further, other additives (adhesive resin powder for further improving the adhesion to the base material, other polymer powders, etc.) may not be blended with the EVOH powder as long as the object of the present invention is not hindered. Be free.

Powder coating in the present invention, spraying method, rotational molding method,
The coating is performed by a fluid immersion method, an electrostatic method, or the like, and among these, coating by a thermal spraying method is particularly preferable. The thermal spraying method is a method in which a powder resin is sprayed from a nozzle onto a substrate surface together with a flame and fused, but when the EVOH powder is sprayed onto the substrate by thermal spraying and fused, the melting point of EVOH is 150. Since it is up to 200 ° C., there is no need to preheat the EVOH powder, and a cast film having good castability and good surface smoothness can be obtained. The number of coatings by the thermal spraying method and the other methods described above may be one or more if necessary.

In the present invention, as a substrate to be subjected to powder coating,
Metals (steel pipes, steel plates, etc.) are typical examples, and range from simple to complex surfaces such as the inner and outer surfaces of a metal tank, the surface of a pump impeller, and the surface of a metal pipe.

Further, ceramics, ceramics, glass, plastics and the like can be used as the base material.

E. Examples Hereinafter, the present invention will be described specifically with reference to Examples.

Example 1 Rolled steel sheet for general structure (SS41) 70 × 100 mm, thickness 3.2 mm
Preheated to 130-150 ° C., and then saponified EVOH (ethylene content 47 mol%, degree of saponification 99.6 mol%, MI 14 g / 10
Min.), And sprayed on the above iron plate by powder spraying method (preheating: about 100 ° C, powder discharge rate: 150 g / min) using powder that does not pass through the 80 mesh section of 100 mesh mm. The coating surface is extremely smooth, the coating thickness is uniform,
Moreover, the adhesion to steel sheets, water resistance and alkali resistance were also very good as shown in Table 1.

Comparative Example 1 EVOH powder, ethylene content 62 mol%, degree of saponification
Thermal spraying was performed under the same conditions as in Example 1 except that EVOH powder (powder that does not pass through the 15 mesh section) was used at 99.5 mol% and MI of 80 g / 10 min to form a coating film. The sprayed resin had drastic dripping of the molten resin, and the coated surface was not smooth but uneven, and the coating thickness was also uneven. Table 1 shows the water resistance and alkali resistance.

Example 2 As EVOH powder, ethylene content 44 mol%, degree of saponification
Thermal spraying was performed under the same conditions as in Example 1 except that EVOH powder of 99.6 mol% and MI of 5.5 g / 10 min was used to form a coating film. The coated surface was extremely smooth, the coating thickness was uniform, and the adhesion to the steel sheet was good.

Comparative Example 2 As EVOH powder, ethylene content 32 mol%, saponification degree
Except for using 99.6 mol%, EVOH powder (powder that passed through 100 mesh sections) with MI of 1.7 g / 10 min, thermal spraying was performed under the same conditions as in Example 1 to form a coating film. The coating surface had irregularities, and the coating thickness was uneven.

Comparative Example 3 As EVOH powder, ethylene content 30 mol%, saponification degree
Except for using EVOH powder of 96.6 mol% and MI of 2.94 g / 10 minutes, thermal spraying was performed under the same conditions as in Example 1 to form a coating film. The uniformity was also insufficient. The other evaluation results are as shown in Table 1.

Comparative Example 4 EVOH powder, ethylene content 80 mol%, degree of saponification
Thermal spraying was performed under the same conditions as in Example 1 except that EVOH powder of 99 mol% and MI of 70 g / 10 min was used to form a coating film. The coated surface was extremely smooth and the coating thickness was uniform, but the other evaluation results were as shown in Table 1.

F. Effects of the Invention According to the present invention, the adhesiveness with the substrate is improved, the coated surface is smoothed, and the coating film thickness is made uniform, and further, gas barrier properties and solvent resistance are imparted to the substrate surface. I can do it.

Claims (2)

(57) [Claims] 1. Ethylene having an ethylene content of 20 to 60 mol%, a degree of saponification of a vinyl acetate component of 99 mol% or more, and a melt index of 5 to 60 g / 10 min (a value measured under a load of 2160 g and a temperature of 190 ° C.) -A powder coating resin comprising a saponified vinyl acetate copolymer and having a powder particle size of 20 to 100 mesh. 2. A resin for powder coating by the thermal spraying method comprising the resin according to claim 1.